In a mobile communication network such as UMTS, UE (User Equipment) is provided with a Limited amount of power for transmitting different class of logical traffic channels during an uplink communication. Each logical channel transporting different services and/or signalling data which necessitates specific rate and/or QoS (Quality of Service).
At each elementary transmission time interval (TTI), the UE selects a sub-rate for each channel by selecting a TFC (Transport Format Combination).
The selection of the TFC (Transport Format Combination) to be used in the uplink during each TTI is under the control of the MAC (Medium Access Control) layer of the UE which selects the TFC according not only to the data available to be sent and the priority of the flows to which the data belongs, but also to a maximum transport block size communicated by the Base Station, which depends on the conditions of the radio channel.
According to the current selection scheme, a User Equipment must report to the Base Station the reporting is properly defined both in terms of content and triggering.
Since the mobile may have several data flows running at the same time (i.e. several radio bearers) it is important that the content of the BSR takes into account the data queues associated to each bearers, but at the same time tries to reduce the amount of information sent to the network in order to reduce the signaling overhead. Hence there is a compromise between the level of detail contained in the BSR and the amount of resources needed to send this BSR.
Moreover, in order to reduce signaling overhead, it is felt sensible not to send the BSR at each transmitting occasion (each TTI). Instead, a number of triggers are defined in order to send the BSR when really needed.
It is to be noted that the current 3GPP standard specification requires that a BSR is triggered in the following conditions:
a—If the UE has no resource to transmit, and some data arrives in one of the queues, the BSR is triggered,
b—If data with higher priority than the data already in the transmission buffer arrives, the BSR is triggered,
d—A BSR is triggered when a serving cell change occurs,
e—Periodic trigger of the BSR may also be configured by higher layers.
Moreover, in the current LTE MAC specification (36.321 v2.0.0 December 2007), a BSR shall be reported if uplink data arrive in the UE transmission buffer and the data belong to a logical channel, group with higher priority than those for which data already existed in the UE transmission buffer.
As it is, this condition does not take into account the PBR (Prioritized Bit Rate) concept introduced in LTE over HSUPA to avoid starvation of lower priority radio bearers.
Specifically, this PBR concept means that some part of the data possibly queued in a LCH (logical channel) of less priority (or in a LCH group of less priority) than another LCH (or LCH group) must actually be treated with a higher priority than the part of the data exceeding the PBR of higher priority LCH's (or LCH groups).
Consequently, there is no warranty that enough resource will be left by the Base Station to ensure the transmission of data queued in a LCH (logical channel) of less priority.
It is therefore desirable to add additional trigger(s) to take into account the PBR concept to avoid starvation of lower priority radio bearers problems.
Document US 2007/0177536 A1 discloses a method for scheduling uplink resource for uplink transmission in which a timing for collection of metrics regarding resource consumption is decoupled from a timing for generating scheduling grants to allow a scheduler to collect the received data information from a plurality of users that have sent E-DCH data within one transmission time interval (TTI) in order to get information of the sum of all users to make a correct decision.
Document EP 1 643 690 A1 discloses a method for scheduling in a mobile communication system a plurality of priority flows data transmitted by a plurality of mobile terminals via a plurality of dedicated uplink channels to a base station.
The method described in this document consists in providing the scheduling base station with QoS information of respective uplink priority flows.